1. Technical Field of the Invention
The present invention relates to a light emitting apparatus including a light emitting element and a phosphor which converts the wavelength of light emitted from the light emitting element, a phosphor for a light emitting element, and a method for producing a phosphor. The present invention particularly relates to a light emitting apparatus including a semiconductor light emitting element, such as LED and LD, for example, and a nitride group phosphor which absorbs a part of light emitted from the light emitting element and converts it into light with wavelength different from the absorbed light.
2. Description of the Related Art
A light emitting apparatus has a structure for obtaining various types of chromaticity, such as white light, with a light emitting element which emits primary light, and a predetermined phosphor which absorbs a part of the primary light and emits secondary light the wavelength of which is longer than the primary light (for example, Patent Document 1). This type of light emitting apparatus mixes the light with converted wavelength and the light from the light emitting element the wavelength of which is not converted, and radiates the mixed light by the combination of the light emitting element and the predetermined phosphor. For example, a white LED light emitting apparatus, which has a blue light emitting diode (hereinafter, occasionally referred to as an “LED”) and a phosphor member coating thereon, has been in actual use. The blue light emitting diode employing an InxAlyGa1−x−yN (0=x, 0=y, x+y=1) group material is used as a light emitting element. The phosphor member is composed of a transparent material, such as an epoxy resin, containing an Yttrium aluminum garnet (hereinafter, occasionally referred to as “YAG”) group phosphor represented by the formula (Y,Gd)3(Al,Ga)5O12. The luminescent color of the white LED light emitting apparatus is obtained based on the additive color mixture principle. After the blue light emitted from the LED enters into the phosphor member, it is repeatedly absorbed and scattered in its layer, and then is outwardly radiated. On the other hand, the blue light absorbed by the phosphor serves as an excitation source, and exhibits yellow fluorescence. Human eyes recognize the mixture of the yellow light from the phosphor and the blue light from the LED as white.
The LED light emitting apparatus using such an LED is small, high effective in terms of electric power consumption, and emits vivid color light. Since an LED is a semiconductor element, it is less prone to burn out. In addition, it has features, such as excellent initial drive characteristics, resistance to vibration or ON/OFF repeats. Since LEDs have these excellent characteristics, LED light emitting apparatuses are used as various kinds of light sources.
On the other hand, in phosphors used for these light emitting apparatuses, various technical improvements are made to improve their durability depending on their applications, or the like (for example, Patent Document 2).                Patent Document 1: Japanese Patent Laid-Open Publication TOKUKAI No. 2003-34791        Patent Document 2: Japanese Examined Publication TOKUKOU No. HEI 7-5884        